The invention relates to a process and apparatus for purifying and conditioning water vapor containing gas streams. The integral hollow fiber membrane gas dryer and filtration device of this invention is particularly useful in removing suspended matter and dehydrating compressed air streams.
Various hollow fiber membrane devices have been used to remove moisture from water vapor containing gas streams. The water vapor containing gas stream is brought into contact with one side of a permeable membrane with a pressure differential being maintained across the membrane, wherein the highly permeable water vapor will permeate the membrane to the second side thereof, and a dry nonpermeate gas is recovered.
It has been known in the art that hollow fiber membrane gas dehydration devices can function more efficiently under some process conditions when a small portion of the dried product gas, i.e., the nonpermeate gas, is recycled as a sweep gas to the permeate side of the membrane. The use of the dry sweep can improve the product gas dryness and/or the productivity of the membrane device. The separation assembly that provides for sweep or purge gas utilization is generally comprised of an annular hollow fiber membrane bundle in an enclosure or shell having a fluid feed inlet, a nonpermeate outlet, a permeate outlet and a sweep gas inlet. Examples of such membrane assemblies can be found in U.S. Pat. Nos. 3,499,062; 3,735,558; 4,718,921; 5,108,464 and 5,026,479. These devices, however, require the use of external plumbing and valves to regulate the flow of the sweep gas that is fed into the sweep gas inlet port. The need to manifold the dry sweep gas externally to the gas separation apparatus adds to the size and complexity of the device. Several attempts have been made to provide a gas dehydration device with an integral internal sweep arrangement, as disclosed in U.S. Pat. Nos. 5,411,662 and 5,525,143.
The membrane gas dehydration devices are usually utilized as a part of an overall gas conditioning system and are thus frequently used in conjunction with filters, coalescers and cyclone separators that are designed to remove suspended matter, particles, and oil and water droplets from the gas stream. These filters and coalescers are typically employed in front of the membrane gas dehydrators, thereby serving to protect membranes against fouling and extending the life of the membrane device. Attempts have been made to integrate these gas-conditioning devices into a single apparatus. An apparatus for air dehumidification that combines a membrane dehydration element with a cyclone separator and a sequence of filters is disclosed in U.S. Pat. No. 6,019,822. However, the apparatus is complex; the filters and the membrane gas dehydration element are disposed so that the longitudinal axis of these elements is parallel to each other. The resulting apparatus is essentially a fusion of conventional sequential filtration elements and a membrane dehydration element packaged into a complicated assembly with little or no associated cost reduction. Thus there still remains a need in the art for an improved gas-conditioning device that simultaneously removes suspended matter and dehydrates the gas.
It is therefore an object of this invention to provide an integral hollow fiber membrane dehydration and filtration device packaged into a casing.
It is another object of this invention to provide an improved process for purifying compressed gas stream by removing suspended matter, such as one or more of oil, water droplets, dust or water vapor with an integral filtration/membrane dehydration apparatus.
According to one preferred embodiment of the present invention, the above objectives and other objectives that are apparent to those skilled in the art may be achieved by a gas purification apparatus comprising:
(i) a housing body defined by a bowl or shell connected in a sealed and removable manner in correspondence with its axial end portion to a head closure member, wherein said head closure member having formed therethrough a feed gas inlet port in a first end of said head closure member and an outlet product port in a second end of said head closure member and a gas flow conduit positioned coaxially to said housing body such that said inlet port and said outlet port are spaced essentially in a straight line relative to one another and said gas flow conduit is placed in fluid communication with said outlet port, and wherein said bowl or shell being provided with at least one waste fluid exit port placed coaxially to said housing body,
(ii) a gas filtration element disposed coaxially in said housing body in fluid communication with said feed gas inlet port, and
(iii) a hollow fiber membrane gas separation cartridge (which is preferably substantially cylindrical) disposed coaxially in said housing body downstream of said filtration element and connected in a sealed and removable manner with its first axial end to said gas flow conduit in the head closure member and with its second axial end to said waste fluid exit port in said bowl or shell.
A more preferred hollow fiber membrane cartridge includes:
a) an elongated tubular inner core member,
b) a substantially cylindrical hollow fiber membrane bundle surrounding said inner core member constructed from hollow fiber membranes having permeate and nonpermeate sides, said bundle being characterized as having a substantially countercurrent flow arrangement between the gas flow on said permeate side and the gas flow on said nonpermeate side,
c) two tubular tubesheets encapsulating both ends of the hollow fiber bundle in a fluid-tight arrangement with one end of the inner core member opening out of one of the tubesheets to permit flow of gas in and out of said inner core member and wherein at least one of said tubesheets is severed to permit an unobstructed flow of gas in and out of the hollow fiber lumens; and,
d) a shell and at least one end closure surrounding said hollow fiber membrane bundle.
Preferably the cartridge is further provided with a flow-control orifice that channels a fraction of the nonpermeate gas as a sweep to the permeate side of the hollow fiber membranes.
According to another preferred embodiment of this invention, the above objectives and other objectives that are apparent to those skilled in the art are achieved by providing a gas purification apparatus comprising:
a) a housing body defined by first and second essentially cylindrical bowls or shells connected in a sealed and removable manner in correspondence to their axial end portion to a common head closure member being interposed therebetween, said first and second bowls or shells defining a lower internal chamber and upper internal chamber within said housing, wherein said head closure having formed therethrough a feed gas inlet port in a first end of said head closure and a product outlet port in a second end of said head closure, such that said inlet port and said outlet port are spaced essentially in a straight line, and at least one gas transport conduit in fluid communication with said upper and lower internal chambers and wherein said first bowl or shell and said second bowl or shell being provided with at least one waste fluid exit port,
b) a gas filtration element adapted to separate liquid and solid particles from incoming gas passing therethrough disposed in said lower chamber, and
c) a substantially cylindrical hollow fiber membrane cartridge adapted to separate water vapor from incoming gas passing therethrough disposed in said upper chamber.
Wherein said filtration element and said hollow fiber membrane cartridge are disposed around a common longitudinal axis within said housing body, said axis being essentially concentric to said housing body.
According to another preferred embodiment of the present invention, the above objectives and other objectives that are apparent to those skilled in the art are achieved by providing a gas purification process comprising:
a) passing a feed gas stream containing water vapor through at least one filtration element adapted to separate liquid and particulates from said incoming feed gas passing therethrough,
b) contacting the filtered feed gas with a multiplicity of hollow fiber membranes contained in a cartridge,
c) permeating a portion of the water vapor contained in the feed gas stream through the membranes,
d) utilizing a portion of a resultant nonpermeate dehydrated gas stream internally of the cartridge to provide a sweep gas to the permeate side of the hollow fiber membranes substantially countercurrent to the flow of the feed gas,
e) recovering the main remaining nonpermeate dehydrated and filtered gas stream, and wherein said filtration element and said hollow fiber membrane cartridge are disposed around a common longitudinal axis and are enclosed in a common, essentially cylindrical casing. According to another embodiment of the present invention, the above objectives and other objectives that are apparent to those skilled in the art are achieved by providing a gas purification process comprising:
a) contacting a feed gas with a multiplicity of hollow fiber membranes contained in a cartridge,
b) permeating a portion of the water vapor contained in the feed gas stream through the membranes while simultaneously removing suspended matter contained in said feed gas; and
c) recovering the main remaining nonpermeate dehydrated and filtered gas stream.
A portion of a resultant nonpermeate dehydrated gas stream may be used internally of the cartridge to provide a sweep gas to the permeate side of the hollow fiber membranes substantially countercurrent to the flow of the feed gas stream.